Geiger-muller counter



Filed bot. 27, 1 944 INVl-JVTOR. A1. am? .51 Mrs TON Air-onus;

Patented Oct. 15,1946

Albert s. Keaton, New York, N. Y. Application October 21, 1944, Serial No. 560,668

4 Claims. 1

This invention relates to the measurement of radioactive substances, X-rays and other ionizin radiation, and more particularly it relates to a stable self-quenching counter of the Geiger- Miiller type.

The tubes of self-quenching Geiger-Muller counters are generally filled with a mixture of ases, such as air and argon, or a mixture of an organic vapor such as alcohol and a permanent gas such as argon. Such counters are generally usable over shorter or longer ranges of voltage.

An object of this invention is to provide a new and improved counter of the Geiger-Muller type.

Another object of this invention is to provide a counter which is easy to make and of long life.

A further object of this invention is to provide a counter which has good resolving power.

A further object of this invention is to provide a counter which is usable over relatively broad ranges of voltage.

A still further object of this invention is to provide a counterwhich gives no change of count with increased voltage over certain regions.

- Other and additional objects will appear hereafter.

The objects of this invention are accomplished, in general, by filling the tube of a Geiger-Muller counter with the vapor of an. organo-metallic compound.

The present invention will be more clearly understood by reference to the following detailed description when taken in connection with the accompanying drawing, in which:

Figure 1 is an elevation of one form of Geiger- Mi'iller counter embodying the features of this invention; and

Fi ure 2 is an elevation of another form of Geiger-Muller counter embodying the features of this invention.

Referring now to the drawing wherein like reference numerals designate like parts, the refer- In an illustrative procedure for making the counter tube above described, the cylinder l2 and the wires l4 and 20 are assembled in the tube III as shown in the drawing. The tube is evacuated with a single-stage mercury pump from an opening, designated by the reference numeral 30. After evacuation to the desired pressure, tetramethyl lead vapor is permitted to flow into the tube lllfrom a, reservoir, the reservoir containing the tetramethyl lead having been previously evacuated without first freezing the compound so that any volatile impurities would be removed.

Because of the toxic properties of the tetramethyl lead, a cold trap is inserted between the oil pump and the mercury pump so that none of the vapor will leak out into the room or into the oil pump. After the required quantity of tetramethyl lead is introduced, the opening 30 is sealed.

In another embodiment of the invention and as shown in Figure 2, the cylinder I2 is omitted and the wall of the tube l0 sllvered. In this embodiment, the wire 14 is secured to the silvered wall of the tube In. The tube I 0 is approximately /4 of an inch in diameter, and the tungsten wire 20 is 4 mills in diameter. A tube of such dimensions is filled with tetramethyl lead to about 1.8 to 2.0 cm. pressure by the same process previously described. This pressure gives good sensitivity and its usable voltage range starts at about 1500 volts.

The usable voltage range for most of the silvered wall counters containing 1.8 to 2.0 cm. pressure is more than 500 volts. The counters of the instant invention, in addition, show ranges of 150 to 250 volts even with moderately fast counts where there is practically no change in count with voltage. Unlike argon-alcohol counters, which show a very steep rise from threshold to plateau, the instant counters require a much larger change in voltage to get from threshold to plateau. The tetramethyl lead counters show their plateaus even after extended use.

Though in the preferred embodiment of the invention tetramethyl lead is preferred, it is understood that the invention is not restricted to such specific metal alkyl. In general, other metal alkyls, such as, for example, dlmethyl mercury, can be used. As shown by the periodic system, the metals of the metal alkyls (organometallic compounds) herein disclosed are members of series 9 having an atomic weight of at least 200 and are non-radioactive. Instead of using tetramethyl lead alone, a mixture thereof with an organic vapor, such as ethyl alcohol, may also be used. An illustrative example of such a mixture may comprise (mol) of tetramethyl lead and 50% (mol) of alcohol at a total pressure of 2 cm. Another mixture containing tetramethyl lead, ethyl alcohol and argon also has given good results. An illustrative example of 3 such mixture comprises 10% or tetramethyl lead, 80% 0! Ion and 10% of alcohol at a total D sure of 10 cm.

In the specific embodiments hereinbefore described, the tubes were iilled to a pressure of 1.8 to 2.0 cm. (mercury). Theinvention is not restricted to such pressure range. In general, satisfactory results are obtained when the pressure is from 0.8 to 2.5 cm. (mercury) or even higher, 1. e. higher temperature when the vapor pressure of tetramethyl lead is higher.

In one or the foregoing speciiic embodiments of the invention, the cylinder I! was described as beingmade 01' silver and the wires 14 and 20 as being madeior tungsten. It is to be understood that the invention is not restricted to such specific materials. The cylinder I! may also be formed of silver-plated metals, gold, gold-plated metals. platinum, etc.; and the wires may be formed of other conducting materials. Similarly, the tube II, which is preferably made of glass. may be made or any insulating material. In that embodiment of the invention wherein the cylinder I! is omitted, the tube it may be made of metal or, when made of glass or other insulating material, may be provided with a conducting metallic surface.

It is to be understood that the invention is not restricted to any precise form and construction of counters but is, in general, applicable to all such counters.

The instant invention provides a self-quenching Geiger-Muller counter characterized by high resolving power, long pateaus and good sensitivity, and having wide ranges where the counter is practically independent 01 the voltage applied to the tube. The counters oi the instant invention may be used in the same manner and for the same purposes for which Geiger-Muller counters are used.

Since it is obvious that various changes and modifications may be made in the above description without departing from the nature or spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

' I claim:

1. A Geiger-Muller counter tube filled with a vapor comprising an organo-metallic compound consisting of an alkyl compound of a non-radioactive metal of series 9 of the periodic system and having anatomic weight of at least 200.

2. A Geiger-Muller counter tube filled with a vapor comprising an organo-metallic compound consisting of a methyl compound oi a non-radioactive metal of series 9 of the periodic system and having an atomic weight of at least 200.

3. A Geiger-Muller counter tube filled with a vapor comprising tetramethyl lead and under a pressure or from 0.8 to 2.5 cm. (mercury).

4. A Geiger-Muller counter tube tilled with a vapor comprising tetramethyl lead and under a pressure oi from 1.8 to2.0 cm. (mercury).

ALBERT B. KESTON. 

